1. Field of the Invention
The present invention is directed to a cutting head for an electric shaver, and more particularly to a cutting head designed for effectively shearing long or fuzzy hairs
2. Description of the Prior Art
For attaining effective shearing of long or fuzzy hairs there have been provided cutting heads which utilize a hair scooping projection added to an inner blade in hair shearing relation with an outer shearing foil. Typical example of the cutting head with the above hair scooping projections is disclosed, for example, in Japanese Utility Model early publication (KOKAI) of application No. 58-68267 published on May 10, 1983, and German Pat. No. 1034511. In the prior devices, as exemplarily shown in FIGS. 1 and 2 of the attached drawings, an outer shearing foil 1 for use in an electric shaver of rotary type cooperates with inner blades 3 for shearing hairs entering the apertures 2 in the outer foil 1. Each of the inner blades 3 is provided at of its one end with hair scooping projection 4 which projects in the general direction of movement of the inner blade 3 and which has at its upper end a sloping edge 5 extending from the cutting edge 6 of the inner blade 3 downwardly and outwardly away from the outer shearing foil 1. The hair scooping projection 4 moves along a particular series of the apertures 2 in spaced relation therebelow as the inner blade 3 is driven so that a long hair strand H entering deep through the apertures 2 in that particular series is entrapped by the projection 4 and is guided or slid along the sloping edge 5 upon movement of the inner blade 3 up to the cutting edge 6 at the upper end of the inner blade 3 where it is successfully sheared against the peripheral edge of the aperture 2. Thus, long hairs can be cut to short hairs which are successively sheared by the cooperation of the inner blade 3 with the other apertures in the outer shearing foil 1 during a continuous manipulation of moving the cutter head across the skin of the user, providing a rapid shaving operation. However, in the above prior device, the cutting edge 6 cooperating with said hair scooping projection 4 is in sliding contact not only with the row in which the above particular apertures 2 are arranged but also with a rib 7 separating that row from the other perforated section of the outer shearing foil 1, rendering the device vulnerable to suffer from an increased resistive load.
Another prior cutting head designed for shearing long hair is exemplarily shown in FIGS. 3 to 5, which is of the rotary type and comprises a stationary cutter 10 formed with an inverted U-shaped channel 11 having a series of circumferentially spaced and generally radial slots 12 each extending into the opposite sidewalls of the channel 11. Placed within the channel 11 are inner blades 13 which are biased upwardly by a spring 14 for shearing engagement with the channel 11. The slots 12 are elongated in a generally radial direction but angled with respect to the cutting edge of the inner blade 13 so that the cutting edge progresses along the longitudinal edge of each slot 12 at an optimum shearing angle. With this construction, long hair can be smoothly fed or combed into the channel 11 through the openings in the sidewall thereof so as to be successfully sheared between the inner blade 13 and the channel 11. In this prior cutting head, however, spacings should be required between the longitudinal ends of the inner blade 13 and the opposed sidewalls of the channel 11 in order to compensate for unintended axial misalignment between the inner blade 13 and the stationary cutter 10 due to possible eccentricity of an inner blade assembly or an output rotor shaft connected to an inner cutter assembly carrying the inner blade 13 with respect to the stationary cutter 10. In view of said spacing required in the above device a problem occurs that a long hair strand H combed into the channel 11 is likely to tangle with the opposite sides of the inner blade 14 to be pulled thereby, as shown in FIG. 4, thus adversely affecting the shearing operation and irritating the user.
Another problem concerned with the above device is that a part of the cutting edge of the inner blade 13 may sometimes fall into the slot 12 in the channel 11, as shown in FIG. 5, producing a loud noise due to the excessive engagement between the channel 11 and the cutting edge and further interrupting the motion of the inner blade 13 in extreme condition. That is, when considering that the requirement of giving enough mechanical strength to the stationary cutter 10 of the above type limits the length X of the channel 10 and correspondingly the length Y of the cutting edge of the cooperating inner blade 13 which is oriented at the optimum shearing angle with respect to the length of each slot 12, an index L/Y indicating the risk of the inner blade 13 falling into the slot 12 becomes a large value, where L is an effective length of a segment of the cutting edge appearing in the slot 12 at the optimum shearing angle with respect to the edge of each slot 12, as shown in FIG. 3. Accordingly, the inner blade 13 with less thickness is more likely to suffer from the unacceptable falling of the inner blade 13. If, on the other hand, the inner blade 13 be formed to have a greater thickness T enough for avoiding the above falling of the inner blade 13, the engaging surface of the inner blade 13 with the stationary cutter 10 would be correspondingly increased to thereby unduly increase the resistive load.